Fuel cells produce electricity through electrochemical reaction and have been used as power sources in many applications. Fuel cells can offer significant benefits over other sources of electrical energy, such as improved efficiency, reliability, durability, cost and environmental benefits. Fuel cells may eventually be used in automobiles and trucks. Fuel cells may also power homes and businesses.
There are several different types of fuel cells, each having advantages that may make them particularly suited to given applications. One type is the proton exchange membrane (PEM) fuel cell, which has a membrane sandwiched between an anode and a cathode. To produce electricity through an electrochemical reaction, hydrogen (H2) is supplied to the anode and air or oxygen (O2) is supplied to the cathode.
In a first half-cell reaction, dissociation of the hydrogen (H2) at the anode generates hydrogen protons (H+) and electrons (e−). Because the membrane is proton conductive, the protons are transported through the membrane. The electrons flow through an electrical load that is connected across the electrodes. In a second half-cell reaction, oxygen (O2) at the cathode reacts with protons (H+) and electrons (e−) are taken up to form water (H2O).
In fuel cell applications, a plurality of fuel cells are combined in series to form one or more stacks. Power demands of different fuel cell applications vary. Changing the active area of the fuel cell in a stack can scale power. This approach, however, requires fuel cells to be redesigned and/or retooled for the different power levels, which is a costly approach.
Other ways of scaling the power output of fuel cell stacks include varying the number of cells in a stack and/or connecting stacks in series. When changing stack output voltages, it is usually necessary to redesign supporting components such as compressors. When stacks are connected in series to allow power scaling, different output voltages are produced, which complicates the design of accessory loads and electrical interfaces.